1. Field of the Invention
The present invention relates to a motor drive device, a timepiece device, and an electronic device.
2. Description of the Related Art
An electronic timepiece (a timepiece device) that uses a solar battery or the like as a primary power supply portion is generally known. This sort of electronic timepiece may be, for example, an analog electronic timepiece that uses voltage that is generated by the primary power supply portion to charge a secondary battery (a secondary power supply portion), and that then uses the charged power of the secondary battery to output a motor drive pulse from a timepiece circuit and rotationally drive a motor that operates the hands of the timepiece.
With this sort of electronic timepiece, the output voltage of the solar battery varies drastically according to the intensity of the sunlight, causing the power supply voltage to applied to the timepiece circuit to vary, so the operation of the timepiece circuit sometimes becomes unstable. Accordingly, as disclosed in Japanese Patent Application Publication No. JP-A 62-238484, for example, the power supply voltage for the timepiece circuit may be detected before the motor is driven, a determination may be made as to whether the power supply voltage that is applied to the timepiece circuit is a high voltage or a low voltage, and a suitable pulse width may be selected according to the result of the high voltage/low voltage determination.
However, with the technology that is described in Japanese Patent Application Publication No. JP-A 62-238484, the problems hereinafter described occur. Specifically, with this technology, the power supply voltage for the timepiece circuit is detected before the motor is driven, and the motor drive pulse (a pulse for high voltage or a pulse for low voltage) is selected. Therefore, in a case where the power supply voltage for the timepiece circuit changes suddenly while the motor is being driven, due to a change in the charging state when charging of the secondary battery starts or stops, the possibility exists that the selected motor drive pulse will become unsuitable, that the motor will not rotate, or the like, causing a malfunction in the motor.
In a case where the non-rotation of the motor is detected by a rotation detection technology, it is conceivable that the time error that is caused by the non-rotation of the motor will be corrected by causing the motor to rotate using a drive pulse that has a sufficient width for driving the motor reliably. However, this sort of rotation detection technology detects the rotation/non-rotation of the motor based on the waveform of the voltage that is output to the motor terminal after the drive pulse is output, and it assumes that the variation in the voltage will be comparatively gradual. Therefore, this sort of rotation detection technology is unable to function properly in a situation where the voltage changes suddenly, as it does when the charging of the secondary battery starts or stops in a case where a solar battery or the like is used.
In other words, with the two technologies described above, a problem exists in that the motor cannot operate reliably in a case where the power supply voltage changes suddenly while the motor is being driven, due to a change in the charging state of the secondary battery.